1. Field of the Invention
The present invention relates to an ink jet head, a substrate for ink jet head, an ink jet cartridge, and an ink jet apparatus.
2. Related Background Art
The ink jet recording apparatus conducts recording with a non-impact recording system. The ink jet recording apparatus has characteristics of high speed ink recording, possibility of recording on various recording mediums, and generation of no or little noise. Because of such characteristics, ink jet apparatuses are widely used as a recording mechanism in printers, word processors, facsimiles, copying machines, and so forth.
A typical ink jet recording method employs an electrothermal converting element, and conducts recording by discharging fine liquid droplets through a fine discharge opening onto a recording paper sheet. The ink jet recording head generally comprises an ink-ejecting device for forming liquid droplets and an ink-supplying system for supplying ink to the ink-ejecting device. For example, an ink jet recording head which has an electrothermal converting element in a pressurizing chamber discharges recording liquid droplets by bubbling pressure generated by foaming or boiling of the recording liquid caused by thermal energy given by electric pulses in accordance with recording signals.
The ink jet printer is a superior recording system as mentioned above. However, it involves a problem that the recorded image depends on a temperature of the ink jet recording head. For example, the quantity of ink discharge varies with the temperature of the recording head, resulting in a larger quantity of ink discharge at a higher ambient temperature as is well known. The temperature of the recording head becomes higher during recording, which varies the quantity of ink discharge to cause irregularity of printing density due to the temperature difference between at the beginning of printing and in the course of printing. To solve the problem, one method is elevation of the head temperature to a certain level by reference to the temperature information derived from one or more detection means such as diode sensors provided in the ink jet recording head. Another method is control of the recording liquid around the electrothermal converting element by application of small pulses not causing recording liquid discharge immediately before each discharge.
Such technical methods of temperature control are based on the assumption that the temperature distribution in the ink jet recording head is uniform, or the temperature at portions of the head remote from the sensor is nearly equal to the temperature around the sensor. However, in the recording head in which ink is supplied from an ink tank placed at the back of the substrate as shown in FIG. 8, depending on a type of ink supply opening, plural rows of electrothermal converting elements are thermally isolated from each other, and the heat generated by one row of electrothermal converting elements is not readily transferred to another row of converting elements. FIG. 9 is a front view of a substrate of an ink jet recording head of a prior art. The substrate carrying thereon electrothermal converting elements is usually made from a highly thermal conductive silicon. However, as can be seen from FIG. 9, the heat generated at the portion A is transferred to the portion B through the portions P and Pxe2x80x2. Therefore, owing to low thermal conductivity from A to B, heat distribution is liable to become nonuniform in the ink jet recording head.
In an ink jet recording head, electric energy caused by applied pulses is converted by an electrothermal converting element into thermal energy. The thermal energy is not only converted to kinetic energy for discharging ink droplets but also released to the open air, transferred to ink, and remains in the ink jet recording head. The remaining heat is released later to the open air. However, a problem arises in usual printing in which ink droplets are discharged by continuous application of high frequency electric pulses to electrothermal converting elements. Because relaxation time for releasing the remaining heat is longer than cycle time of ink discharge, the heat is accumulated in the recording head and raises the temperature of the recording head. The accumulated heat causes the problem as below.
Initially the rise of temperature of an ink jet recording head causes change of the ink discharge rate, giving difference of record density between start of printing and just before end of printing. Secondly, frequency and timing of ink discharge varies among the ink jet recording elements when recording signals or electric pulses are applied in a usual manner. The variation of the frequency and timing of ink discharge results in nonuniform distribution of temperature in a recording head owing to the remaining heat. The nonuniform temperature distribution in a recording head causes variation of the amount and rate of discharge of the recording liquid among the ink jet recording elements constituting the ink jet recording head, whereby the recorded image deteriorates locally by the nonuniformity of recording density.
The present invention intends to provide an ink jet recording head which has uniform temperature distribution in entirety by diffusion of heat after ink discharge.
The present invention also intends to provide a substrate for an ink jet recording head, and an ink jet cartridge and an ink jet recording apparatus employing the ink jet recording head.
The ink jet head of the present invention comprises ink discharge openings for discharging ink and a substrate having a plurality of rows in each of which a plurality of electrothermal converting elements for generating thermal energy for discharging ink from the discharge openings are provided and having an ink supply opening between the rows of the plurality of electrothermal converting elements corresponding to length of the row, wherein portions of the substrate having the row disposed the plurality of electrothermal converting elements are connected to each other by a member having a thermal conductivity coefficient nearly equal to or higher than that of the substrate.
The present invention provides an ink jet recording head in which temperature distribution is uniform, and which is capable of forming images with less density irregularity caused by nonuniform distribution of temperature. Therefore, the number of temperature sensors conventionally equipped in the ink jet recording head can be reduced. In a preferred embodiment of the present invention, a wire mesh used as a heat transfer member of the recording head can also serve to remove dust from the recording liquid by filtration.